A method for measuring a direction of eyes of a person, for example a driver, or estimating an awakened level of a person, for example of a driver, by detecting a state of the driver's eyes on the basis of an image of a face (hereinafter referred to as a face image) of the driver is known. In order to determine a state of the driver's eyes, eyes in the face image of the driver need to be accurately detected.
For example, technology for detecting an opened and closed state of eyes is disclosed in JP1998044824A and in JP2001307076A. A known device disclosed in JP1998044824A detects positions of the eyes and sets a target area for executing a detection process of an open/close state of the eyes. The target area includes the positions of the eyes. Then, the known device disclosed in JP 1998044824A calculates a distribution of frequencies of density values within the target area for detecting the open/close state process, and then the known art detects an area of the eyes by determining a peak value in the distribution of the frequencies as a border value. Further, the known device disclosed in JP 1998044824A determines a maximum length of the eye area in a longitudinal direction as size of eyes.
On the other hand, the known device disclosed in JP2001307076A firstly extracts features that correspond to information of eye features in order to detect positions of the eyes of the driver. Secondly, the known art disclosed in JP2001307076A detects an eye opening level and positions of upper eyelids based on changes of detailed density of the eyes within an target area in which the eyes are included. Thirdly, the known device disclosed in JP2001307076A measures a positional distance in a vertical direction between predetermined positions of the upper eyelids and a fixed standard feature of the face around the eye, for example nostrils, on the basis of the positions of the eyes or the detailed density of the eyes. Then, the known device disclosed in JP20013007076A determines the opened/closed state of the eyes on the basis of the opening level of the eyes and the positional distance in the vertical direction.
According to the known devices disclosed in JP1998044824A and JP2001307076A, because those known devices detect the eyes within the face area it takes time to detect the eyes, and further, error may occur in detection of the eyes. For example, the known art described in the JP19980442824A detects the eyes based on the assumption that the driver has a certain shape of eyes, for example, eyes whose upper eyelids are arch-shaped. Hence, the known device disclosed in JP19980442824A may have difficulties in detecting the eyes in the face image when the driver has narrow eyes or thick eyebrows. Further, when the position of the eyes is detected on the basis of a positional relationship between the eyes and the eyebrows, or between a nose and a mouth, another process for distinguishing the eyes from the eyebrows may be needed.
On the other hand, when the method for firstly determining the eyes in the face image is adopted, it may take time before the known arts determine that the eyes are not detected because of, for example, the driver wearing sunglasses. For example, the known device disclosed in JP2001307076A detects, firstly the positions of the eyes, secondly the known device detects the nostrils based on the positions of the eyes, then the known art determines the opening level of the eyes on the basis of the positional relationship between the eyes and the nostrils. Hence, there may be possibilities that the known at mistakenly determines the eyebrows as the eyes, or nose pads of glasses as the nostrils. The known art disclosed in JP2001307076A determines the darkest density parts as the nostrils in order to distinguish the nostrils from wrinkles around the nostrils shown in the face image. Hence, the known device disclosed in JP2001307076A may not distinguish the nostrils from the nose pads of the glasses, because the nose pads of the glasses may have the similar density level as that of the nostrils.
A need thus exists to provide an eye detecting device which is not susceptible to the drawback mentioned above.